Tuesday, 26 April 2016

Infrared 'faux colour' video from an IR-converted (720 nm) DSLR and Final Cut Pro X

Shortly after my new-to-me infrared-converted (720 nm filter) Nikon D7100 arrived the week before last, I realised that I could try to make 'faux colour' infrared full hd videos. However, I had no idea whether with the software available I could process the footage. A day or two later a spell of wall to wall sunshine arrived and so I wandered down to the Auld Brig o'Doon and stuck my camera over the wall just to get some footage to import in Final Cut Pro X. In the interests of health and safety I did stand well away from the carriageway just in case a drunk came by on a horse pursued by witches who gather at intervals at Alloway's Auld Kirk.

Safely back home, I imported the footage into FCPX and found that converting the footage was actually easier than doing the same job with still photographs using the widely-known techniques and which I have written about at length in previous posts.

I have had installed for some time the excellent and free colour effects plugins produced by Alex Gollner (Alex4d). Included in that bundle is Channel Mixer a4d and with that plugin the red and blue channels can be reversed to produce the blue sky effect. Very soon I had worked out a protocol that worked best for me, with the proviso, of course, that other settings and effects could be applied to produced a whole range of 'looks' in the final output.

To explain what I have been up to I have made a short video which explains the steps in Final Cut Pro X:

I shall not repeat the procedure here but there are a couple of things to point out. Whoever converted the camera for the previous owner managed to set a custom white balance. The raw footage has that white balance applied. Others have found it extremely difficult to set a custom white balance in an infrared-converted D7100, and I have not yet found a way. The 'Balance Colour' first step of the conversion process is, therefore, on footage being taken with the custom white balance. Without a custom white balance, (i.e. white balance on 'auto' on the camera) I cannot get reasonable colour using the Channel Mixer; in these circumastances 'Balance Colour' does a reasonable job to bring the white balance back in line but not quite a good enough one. Therefore, a custom white balance set as advised for the particular IR filter on the sensor would appear to be essential.

I should also point out that my experience is confined to infrared-converted cameras, and does not extend to those uncoverted cameras with an infrared filter attached to the lens.